Potted ballast transformer



United States Patent 3,403,367 POTTED BALLAST TRANSFORMER Robert D.Holzinger, Homcwood, Ill., assignor to The Sherwin-Williams Company,Cleveland, Ohio, a corporation of Ohio No Drawing. Original applicationFeb. 19, 1963, Ser. No. 259,725. Divided and this application Jan. 19,1967, Ser. No. 642,255

1 Claim. (Cl. 336-96) ABSTRACT OF THE DISCLOSURE A ballast transformerhaving a laminated core with insulated wire wound thereon. Surroundingthe transformer is a potting composition comprising 8 to 18 parts ofoiticica oil, from 6 to parts of triisobutylene monomers, from 1 to 8parts of liquid extender and from 70 to 80 parts of a solid particulateextender and ferric chloride catalyst in an amount sufficient to causepolymerization between the oiticica oil and the triisobutylene monomersin an addition polymerization reaction.

This is a division of application Ser. No. 259,725, filed Feb. 19, 1963.

This invention relates to compositions for use in electrical devices,illustratively, which are adapted to impregnate and hold electricallyconductive elements within a case or housing. The compositions functionsto im mobilize the conductive elements and dampen unwanted vibrations.

More specifically, this invention relates to organic insulating gelsproduced in situ by metal chloride catalyzed copolymerization ofisobutylene monomers with conjugated drying oils.

Transformers provide a preferred illustrative use of the invention.Transformers encased and immobilized as hereinafter described are oftencalled potted transformers and compositions used for encasing theelectrically conductive elements of transformers are referred to in theart as potting compositions. Additionally, transformers ofthe type whichare employed in the ballast circuit of fluorescent lights have beenselected for description. Suchv transformers, called ballasttransformers, are of potted construction and are a part of a fluorescentlamp fixture ballast circuit, serving to preheat the cathode of thelamp. Preheating the cathode permits a lower starting voltage thanotherwise operable.

Transformer ballasts are a necessary component of every modernfluorescent lamp circuit. Thus they are mass produced and minoreconomies in the cost of manufacture are important factors.

Asphaltic compositions have heretofore been widely used in the art as afiller for ballast transformers because they are low cost. Althoughasphaltic potting compositions are serviceable under normal operatingconditions, they are thermoplastic and melt readily if heat is generatedabove normal load as when under shorted conditions. Temperatures withina ballast transformer may reach as high as 550 F. Low melting orthermoplastic ballast compositions including asphalt when liquified byheat due to short circuits often leak from the ballast case to damagefloors, rugs, furniture, etc.

A principal object of this invention is to provide a low costthermosetting potting composition for encapsulating electricalconductors in an insulating medium.

Another object of this invention is to provide low-cost pottingcompositions characterized by little viscosity loss when overheated forencasing fluorescent ballast transformer element.

'In practicing this invention, all the ingredients are thoroughly coldblended prior to filling into ballast transformers or other electricaldevices to be encapsulated.

The filled cases are then baked, preferably at about 200 F. for /2 hour,in order to obtain a satisfactory jell.

The ingredients, which according to the preferred form of this inventionincludes isobutylenes, conjugated drying oils, liquid extenders, solidparticulate extenders and a metal chloride catalyst, may be cold blendedas required for use in the filling process. The liquid ingredients mayalso be preblended and stored for later use. It is not recommended thatthe potting composition be completed and stored for an extended periodprior to filling because the action of the catalyst may cause a jell toform before the material can be used. Also, the particulate extender isnot mixed and stored with the liquid materials for long periods becauseextended storage may result in hard settling with consequentdifficulties in redispersing the extender.

The jelled product which is the result of the catalyzed copolymerizationof isobutylenes and conjugated drying oil has the appearance of a Factice and its characteristics are such that it may be used withoutmodification as a potting composition with good results. However,without the incorporation of extenders the cost of this material is notcompetitive with the low cost thermoplastic compositions hereindescribed. Liquid or solid extenders may be incorporated in sufficientconcentration to permit the formulation of economically competitiveballast compositions Without impairing the desirable qualities of theFactice base composition.

In addition, inclusion of solid extenders improves the heat transfercharacteristics of the jelled potting composition so that parasitic heatis more effectively dissipated from ballast units heated duringoperation. Liquid extenders, although they permit economies, must beused with care as they contribute plasticity to the mass. Action of theplasticizer is multiplied considerably at elevated temperatures whichoccur, for example, within a transformer under shorted conditions. Useof liquid extenders in controlled amounts is understood in the ballastart. By control of the amount of metallic chloride catalyst, the jell orFactice may be formed either with or without the presence of liquid orsolid particulate extenders. The compositions thus produced are cured byheating and have a rubber-like quality which serves as an excellentmedium for damping vibrations. Their dielectric strength is sufficientfor use in low voltage transformers without promoting malfunctionthereof due to leakage of currents through the composition.

The term isobutylenes has been used herein to embrace a commercialmixture of predominantly two classes of monomeric materials;diisobutylene and triisobutylene. Isobutylenes may be copolymerizedadmixed or as separated fractions with certain unsaturated fatty dryingoils to form the factice potting composition of this invention. Theterms diisobutylene and triisobutylene signify particular mixtures ofolefinic compounds. Diisobutylene, for example, is described asconsisting of about weight percent of 2,4,4-trimethylpentene-l and about23 weight percent of 2,4,4-trimethylpentene-2- with the remaining 2%consisting of mixed octene isomers. Properties of commercialdiisobutylene are reported as follows:

Specific gravity -at 60 F. 0.7227

Bromine No. 138

Boiling range:

Initial F 214.7 10% F 215.8 30% F 216.1 50% F 218.3 F 218.3 Dry point F220.1

Molecular weight, average, calculated 112.1 Viscosity at 77 F.centistokes 0.7086 Flash point (open cup method) F., min

Triisobutylene is described as consisting of two principal ingredients,2,2,4,6,6,-pentamethyl-heptene-3,

and 2-neopentyl-4,4-dimethylpentene-1. Properties of commercialtriisobutylene are:

Specific gravity at 60 F 0.7640

Boiling range:

Initial F 348.1 10% F 350.2 30% F 351.1 50% F 351.9 90% F 353.1 Drypoint F 354.6

Molecular weight, average, calculated 168 Tung oil and oiticica oil formexcellent jells with isobutylenes and are preferred drying oils forpractice of this invention. Drying oils may be classified generally astriglycerides of long chain fatty acids.

The fatty acid groups in oticica oil and tung oil consist primarily ofgroups containing conjugated unsaturation. Oiticica oil contains about75% licanic acid, an aliphatic acid which contains three conjugateddouble bonds in the 9-10, 11-12 and 13-14 carbon positions of the fattyacid chain. Tung oil contains about 70% to 80% of eleostearic fatty acidgroups which also have three conjugated double bonds at the 9-10, 11-12;and 13-14 carbon positions. With respect to the amount of availableconjugated unsaturation, tung and oiticica oil are unique amongcommercial drying oils. Common drying oils, such as soya and linseedoil, do not contain conjugated fatty acid groups. The less populardrying oils that contain conjugated unsaturation fall short of equallingthe concentration of conjugated unsaturation of tung or oiticica oil.Dehydrated castor oil contains an appreciable quantity of conjugatedfatty acid groups in the glyceride, but the percentage is believed to beabout of the total fatty acid content. While dehydrated castor oil maybe made to jell with isobutylenes, the reaction occurs less readily thanwith tung or oiticica oil. Blown linseed oil among other treated oilshas been polymerized with isobutylenes to form a jell but is inferiorfor the present purposes. Similar treated oils, in addition to inferiorquality of final product, are also of less commercial interest becauseof their higher cost, a factor which is especially limiting with respectto dehydrated castor oil.

Other drying oils which do not contain conjugated unsaturation maycontain a considerable amount of nonconjugated unsaturation.Nonconjugated unsaturation is usually divided among the several types offatty acids forming substantially all the total drying oil fatty acidgroups present in the glyceride oils and containing from one to threedouble bonds per fatty acid hydrocarbon chain. Oils of this type such assoya or linseed oil are slower drying than tung or oiticica oil andattempts to jell them with isobutylenes in the presence of ferricchloride catalyst have been unsuccessful. Evidently, the nonconjugated,unsaturated groups are not sufliciently reactive to copolymerize withcommercially available mixed isobutylenes. The reactants describedherein form a solid factice within /2 hour at a temperature averagingabout 200 F.

Paraffin oils, nondrying fatty oils and drying oils without conjugatedunsaturation as mentioned above may be added to the reaction mixture asliquid extenders or diluents for the essential reactants withoutmaterially interfering with the factice-forming capabilities of oiticicaoil and tung oil with isobutylenes. The amount of liquid diluent andsolid particulate extender which may be incorporated depends uponfactors including the temperature of reaction, proportions of thevarious reactants, maximum in-service temperature requirements, etc.,and it is within the skill of the art to adjust the proportions in orderto influence cost, performance, etc., within the scope of the disclosureand guided by the examples herein set out. As in all formulativeendeavor, exacting requirements require testing procedures to determinewhether the resultant quality meets the requirement in a given case.

A small quantity of inhibitor may be used to prevent local gelationduring catalyst addition. This precaution is particularly expedientwhere the most active reactants, tung oil and triisobutylene, areemployed. Long chain alcohols, illustratively octyl alcohols, aresuitable inhibitors for this purpose.

In the practice of this invention, ferric chloride has been used as thepolymerization catalyst although it is contemplated that other wellknown prior art addition type catalysts including AlCl and B1 areuseful. Metallic chloride addition polymerization catalysts are wellknown. Catalysts for this purpose are referred to, for example, in US,Pat. 2,127,811 including halides of the 2nd or 3rd group of the periodicsystem. Anhydrous boron trifiuoride is described as being very active,polymerizing successfully less reactive semidrying oils. Anhydrousstannic chloride is also reported as an active member of the class.

Effective catalyst concentration for a particular formulation dependsupon several variables including the nature and concentration of thereactants, temperature, extenders, etc. Where large amounts ofparticulate extenders are used, the amount of catalyst is increased asadsorbed moisture introduced into the system by the extender partiallydestroys catalysts strength. Also, the quantity of effective catalyst isfurther reduced because of the tendency of fine particle extenders toadsorb catalyst at their surface. In use of ferric chloride as thecatalyst, optimum catalyst range for commercial purposes was aconcentration of from 0.5 to 1.5% ferric chloride on the total reactantsolids.

With catalyst content adjustment, isobutylenes will copolymerize andform a jell with fatty drying oils having the described conjugatedunsaturation over a wide range of isobutylenes to oil ratios. Usefuljels will be formed when the reactants constitute 90% oil and 10%isobutylenes. Conversely, up to 80% triisobutylene monomer with 20% oilare feasible reactant percentages, but as the pot life of thiscombination is short, prompt use is indicated. Diisobutylene has lessreactivity than triisobutylene and it has been found that a maximum of65% monomer may be reacted with 35% oil in order to prepare asatisfactory jell. Economically, it is preferable that isobutylenesconstitute the major portion of the reactants where pot life of themixture is adequate and the end product fulfills essential physicalrequirements. Dissobutylene and triisobutylene are substantialequivalents for the purposes of this invention, but the slowerevaporation rate of triisobutylene is often advantageous. The preferredratios between diisobutylene monomer and fatty oil reactants for use inthis invention range between 50% diisobutylene to 50% oil and 25%diisobutylene to oil. With respect to triisobutylene and fatty oilreactants, the preferred ratios fall between 60% triisobutylene to 40%oil and 25 triisobutylene to 75% oil. Using the above mentionedproportions and catalyst levels, jells may be obtained Within /2 hour bybaking the liquid reaction mixture, but below the decompositiontemperature of the jel. Similar baking schedules are maintained wherethe liquid reactants are a part of a potting composition formulation. Inthis case, the liquid and particulate extenders are mixed with theliquid reactants before baking.

A liquid extender includes nonvolatile inert liquids compatible with thereaction mixture. Suitable liquid extenders include various fatty oilseither drying or nondrying, and hydrocarbon oils either saturated orunsaturated. In addition to acting as an extender for the more costlydiisobutyhue-triisobutylenedrying oil Factice, the liquid extendersfunction in part to prevent potting compounds from hardening andcracking under extended high temperatures of operation. Pottingcompositions employing isobutylenes and oil as the sole pottingcomponent have a tendency to harden and shrink or crack undertemperatures encountered within a ballast transformer which hasdeveloped a short circuit. Stygene R-2 (a resin produced by The ChemfaxCorporation), described as a mixture of polynuclear aromatic-polymers ofpetroleum origin, is a useful liquid extender with desirableplasticizing properties. In preferred formulations, from 3 to of apolynuclear aromatic polymer of this class has been used, based on theweight of the total composition.

Solid particulate extenders are included in potting compositions todisplace a part of the liquid components with less expensive solidsvolume. The solid extender component of the composition may be, forexample, finely ground silica, silicates, calcium carbonate or othersolid inert pigmentary material of the same general quality. Thecomposition, after incorporating the extender but before potting,desirably is of a pourable viscosity yet of sufficiently high viscosityto maintain the extender in suspension. Enough liquid binder componentis included to provide mechanical strength and elasticity to theencapsulating jel surrounding the electrical conductors of the finalunit. Silica flour is most commonly used as a particulate extender inreducing this invention to practice. It has been found that from 70 to75% of this extender may be used with 30 to of the liquid component byweight without adversely affecting the flow of the resulting mixture orelectrical or physical properties of the jel after baking.

The following examples, while not exhaustive, illustrate the best methodof practicing the invention. The nature of the invention permits a widevariation in the choice of ingredients and in the proportions thereof,Exemplary material included in this specification is intended only as aguide to one skilled in the art to formulate potting compositions withinthe scope of the invention having the properties necessary to meetparticular needs.

EXAMPLE I The materials listed below were combined and the reactiveingredients copolymerized to form a thermoset bal- Oiticica oil andliquid extender were Weighed into a container and triisobutylene addedwhile stirring until uniform. Silica flour was added with mixing untildispersed. Lastly, the catalyst solution was added and blended throughthe mixture.

A ballast transformer was filled with the above mixture and baked at 200F. for /2 hour. An excellent jell was obtained which did not soften orliquify when held at 500 F. for four hours. The encapsulating jellmaterial also did not shrink or crack under the test conditions.

EXAMPLE II The following ingredients were mixed in the same manner as inExample I. Filling and baking the mixture in a ballast transformer at200 F. for /2 hour resulted in a potting composition having rubber-likeproperties. At 500 F. the compound did not exhibit any failure due tomelting or cracking.

The above ingredients were thoroughly mixed as follows:

Oiticica oil, triisobutylene and octyl alcohol were added to a containerand mixed until uniform. The silica flo'ur was then added and evenlydispersed in the liquid. After thoroughly incorporating the catalyst,the compound was filled into a ballast transformer.

The above compound jelled when baked in place in the transformer for /2hour at 200 F. However, it had a tendency to exhibit some cracking whentested at 500 F. for four hours.

EXAMPLE IV The ingredients listed below were blended together and testedas follows:

Gms. Silica flour #68 300 Oiticica oil 30 Fish oil 1O Triisobutylene 60Octyl alcohol 1 Catalyst solution 10 The oiticica oil and fish oil wereadded in a container and mixed. Triisobutylene was added slowly to themixture while stirring until uniformly mixed. The octyl alcohol was thenadded followed by addition of the silica flour with mixing until auniform dispersion was obtained.

Catalyst was added and blended in the mixture.

This material was jelled in a container at 200 F. for /2 hour. The jellobtained was spongy in character with less mechanical strength thanExamples 1, II and III. When tested at 500 F. for 4 hours, the pottingformulation did not liquify nor crack. Mechanical strength was less thanin prior examples. While a time and temperature schedule of /2 hour at200 F. fits a particular requirement, obviously equivalent energy inputschedules may be adapted to fit individual consumer requirements.

What is claimed is:

1. A ballast transformer for use in fluorescent lamp ballast circuitsincluding a laminated core of patterned thin iron sheets wound withinsulated wire, said transformer potted in an insulating mediumcomprising 8 to 18 parts of oiticica oil, from 6 to 15 parts oftriisobutylene monomers, from 1 to 8 parts of a liquid extender and from70 to parts of a solid particulate extender and ferric chloride catalystin an amount sufficient to cause polymerization between said oil andmonomers in an addition polymerization reaction.

References Cited UNITED STATES PATENTS 4/1959 Feder 336-96 3/1960 Wigentet al 33696

